Goal of this Lesson:
We will learn how to estimate sums and differences of decimals.
Here is a sample problem: 898.8 - 379.26 = ???
Can you answer that problem?
Bet you can't--but at the end of this lesson you should be able to!
Using Estimations:
Basically there is no one way to get a correct answer when estimating. We use estimates to get answers more quickly. There are 3 methods that can help us get the answer:
Rounding: you can estimate by rounding each decimal to the nearest whole number that is easy to add or subtract in your head.
Front-end Estimation: you can estimate by first adding or subtracting the front digits. Then you add or subtract the next digits.
Clustering: you can estimate by rounding a group of close numbers to the same number.
Refer to the attached powerpoint presentation for an example of each method: Rounding: Round each number to the nearest 10 for easy adding.50.5 + 68.1 = 118.6 actual result; OR
50 + 70 = 120 as estimated
Front End Estimation: add or subtract the front digits, then the next.
42.6 - 21.2 = 21.4 actual result; OR
4-2 = 2 and 2-1= 1 or 21 as estimated
Clustering: rounding a group of close numbers to the same number.
22+21+23 = 63 actual result; OR
20+20+20 = 60 as estimated
Have you figured out the answer to the sample problem yet? Hint : It's easy if you round by tens.
answer: 500 as estimated.
Goal of this Lesson:
We will learn how to estimate sums and differences of decimals.
Here is a sample problem: 898.8 - 379.26 = ???
Can you answer that problem?
Bet you can't--but at the end of this lesson you should be able to!
Using Estimations:
Basically there is no one way to get a correct answer when estimating. We use estimates to get answers more quickly. There are 3 methods that can help us get the answer:
Refer to the attached powerpoint presentation for an example of each method:
Rounding: Round each number to the nearest 10 for easy adding.50.5 + 68.1 = 118.6 actual result; OR
50 + 70 = 120 as estimated
Front End Estimation: add or subtract the front digits, then the next.
42.6 - 21.2 = 21.4 actual result; OR
4-2 = 2 and 2-1= 1 or 21 as estimated
Clustering: rounding a group of close numbers to the same number.
22+21+23 = 63 actual result; OR
20+20+20 = 60 as estimated
Have you figured out the answer to the sample problem yet? Hint : It's easy if you round by tens.
answer: 500 as estimated.
Links: You can use these sites to help you learn more about using estimations.
http://www.mathleague.com/help/decwholeexp/decwholeexp.htm#estimating
http://www.321know.com/est73ax2.htm|
http://www.glencoe.com/sec/math/msmath/mac04/course1/study_guide/pdfs/mac1_pssg03.pdf